Nitric oxide is a signaling molecule your body produces naturally, and it plays a central role in several areas of men’s health: erections, blood pressure, exercise performance, and brain function. It works by relaxing the smooth muscle inside blood vessel walls, which widens them and increases blood flow. That single mechanism has ripple effects across nearly every system in the body, but a few matter especially for men.
How Nitric Oxide Works in Your Body
Cells lining your blood vessels release nitric oxide, which then passes into the muscle cells wrapped around those vessels. Once inside, it triggers a chain reaction that lowers calcium levels in the muscle cells, causing them to relax. The vessel widens, blood flows more freely, and the tissue downstream gets more oxygen and nutrients.
This isn’t a slow, subtle process. Nitric oxide acts within seconds, and the effect is significant enough that blocking its production in a lab setting raises systolic blood pressure by roughly 15 mmHg and diastolic by over 20 mmHg. When nitric oxide production is restored, blood pressure drops back to normal. That gives you a sense of how much your circulatory system depends on this one molecule.
Erectile Function
This is probably why you searched. Nitric oxide is the primary chemical signal that makes erections happen. When you’re sexually aroused, nerve endings and blood vessel cells in the penis release nitric oxide, which triggers a buildup of a messenger molecule called cGMP. That messenger relaxes the smooth muscle in the erectile tissue, allowing blood to rush in and fill the two spongy chambers (the corpus cavernosum). At the same time, the expanding tissue compresses the veins that would normally drain blood away, keeping the erection firm.
Without adequate nitric oxide, this entire sequence stalls. Low nitric oxide bioavailability is one of the most common underlying causes of erectile dysfunction, particularly in men over 40 whose blood vessel function has started to decline due to age, inactivity, or cardiovascular risk factors like high cholesterol and smoking.
Common ED medications work by protecting cGMP from being broken down too quickly. They don’t create nitric oxide themselves. They amplify whatever signal is already there. This is why arousal is still necessary for these medications to work, and why improving your body’s baseline nitric oxide production can complement their effects or, in milder cases, reduce the need for them.
Blood Pressure and Heart Health
The same vessel-relaxing mechanism that produces erections also keeps your blood pressure in check. Nitric oxide continuously regulates vascular tone throughout your body. When production drops, as it does with aging, arteries stiffen and narrow, forcing your heart to pump harder.
Men are at higher risk for hypertension and cardiovascular disease at younger ages than women, partly because estrogen supports nitric oxide production in premenopausal women. For men, maintaining nitric oxide levels through diet, exercise, and avoiding smoking becomes especially important in the 30s and 40s, well before cardiovascular symptoms typically appear.
Exercise Performance and Recovery
Greater blood flow means more oxygen delivered to working muscles, which is why nitric oxide precursors have become popular sports supplements. The research here is more nuanced than the marketing suggests, but there are real findings worth knowing.
Supplementing with L-citrulline (an amino acid your body converts into nitric oxide) at doses of 2.4 to 6 grams per day over one to two weeks significantly increased nitric oxide levels and improved physical performance markers in studies. A single acute dose of L-arginine (another precursor) at 6 grams showed no significant effect on nitric oxide or performance, which highlights an important difference between the two supplements.
Recovery is where the data gets more interesting for anyone who lifts weights. One study of 41 men found that taking 8 grams of citrulline an hour before strength training reduced muscle soreness by 40% at 24 hours and 41% at 48 hours compared to a placebo. A separate trial in sub-elite athletes showed soreness scores dropped by about 23% with citrulline supplementation. The effect likely comes from improved blood flow clearing metabolic waste from muscles more efficiently after intense exercise.
Brain Function and Blood Flow
Nitric oxide also governs blood flow in the brain through a process called neurovascular coupling. When a region of your brain becomes active, local neurons release nitric oxide, which dilates nearby blood vessels and delivers the extra oxygen and glucose those neurons need. This is happening constantly, thousands of times a day, matching blood supply to mental demand in real time.
As nitric oxide production declines with age, this coupling becomes less efficient. The brain doesn’t get blood flow increases as quickly or as precisely where it needs them. This is one proposed mechanism linking cardiovascular health to cognitive decline in older men, and it’s part of why exercise (which boosts nitric oxide) consistently shows benefits for mental sharpness.
Foods That Boost Nitric Oxide
Your body produces nitric oxide through two pathways. The first uses L-arginine directly. The second converts dietary nitrates (from vegetables) into nitric oxide through bacteria in your mouth and chemical reactions in your stomach. Both pathways matter, but the dietary nitrate route becomes increasingly important as you age and the enzyme-based pathway slows down.
The highest-nitrate foods, measured per kilogram:
- Spinach (raw): roughly 2,960 mg/kg
- Beetroot: roughly 2,010 mg/kg
- Parsley: roughly 1,960 mg/kg
- Celery: roughly 1,530 mg/kg
- Lettuce: roughly 1,140 mg/kg
Beetroot gets the most attention because it’s easy to consume in juice form, and concentrated beet juice has been used in many of the exercise performance studies. But raw spinach actually contains about 50% more nitrate per serving. A large salad with spinach, celery, and beets covers a substantial amount of what your body can use.
One important note: antiseptic mouthwash kills the oral bacteria responsible for converting nitrates to nitric oxide. If you’re eating these foods specifically for their nitric oxide benefits, using mouthwash regularly may be undermining the effect.
Supplements: L-Citrulline vs. L-Arginine
L-arginine is the direct precursor to nitric oxide, so it seems like the obvious supplement choice. In practice, L-citrulline works better. When you take L-arginine orally, much of it gets broken down in the gut and liver before it ever reaches your bloodstream. L-citrulline bypasses that breakdown, gets absorbed intact, and is then converted to L-arginine in the kidneys, resulting in higher and more sustained blood levels of L-arginine than taking L-arginine itself.
Study dosages typically range from 3 to 6 grams for L-arginine and 2.4 to 6 grams for L-citrulline. Combining the two appears to increase circulating nitric oxide more effectively than either alone, likely due to a synergistic effect on the production pathway.
Who Should Be Cautious
Because nitric oxide lowers blood pressure, anyone who already has low blood pressure should avoid nitric oxide-boosting supplements. The combination could cause dizziness, fainting, or dangerous drops in pressure. The same concern applies if you’re taking blood pressure medications or nitrate drugs for chest pain, since stacking these effects can be unpredictable.
People with kidney disease or those recovering from a heart attack should also exercise caution. A study published in JAMA found that people taking L-arginine after a heart attack had a higher rate of death and rehospitalization than those who did not. Doctors also recommend stopping nitric oxide supplements before surgery, since the blood pressure-lowering and potential blood flow effects could complicate anesthesia and recovery.